NAME

       SSL_check_chain - check certificate chain suitability

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_check_chain(SSL *s, X509 *x, EVP_PKEY *pk, STACK_OF(X509) *chain);

DESCRIPTION

       SSL_check_chain() checks whether certificate x, private key pk and certificate chain chain
       is suitable for use with the current session s.

RETURN VALUES

       SSL_check_chain() returns a bitmap of flags indicating the validity of the chain.

       CERT_PKEY_VALID: the chain can be used with the current session.  If this flag is not set
       then the certificate will never be used even if the application tries to set it because it
       is inconsistent with the peer preferences.

       CERT_PKEY_SIGN: the EE key can be used for signing.

       CERT_PKEY_EE_SIGNATURE: the signature algorithm of the EE certificate is acceptable.

       CERT_PKEY_CA_SIGNATURE: the signature algorithms of all CA certificates are acceptable.

       CERT_PKEY_EE_PARAM: the parameters of the end entity certificate are acceptable (e.g. it
       is a supported curve).

       CERT_PKEY_CA_PARAM: the parameters of all CA certificates are acceptable.

       CERT_PKEY_EXPLICIT_SIGN: the end entity certificate algorithm can be used explicitly for
       signing (i.e. it is mentioned in the signature algorithms extension).

       CERT_PKEY_ISSUER_NAME: the issuer name is acceptable. This is only meaningful for client
       authentication.

       CERT_PKEY_CERT_TYPE: the certificate type is acceptable. Only meaningful for client
       authentication.

       CERT_PKEY_SUITEB: chain is suitable for Suite B use.

NOTES

       SSL_check_chain() must be called in servers after a client hello message or in clients
       after a certificate request message. It will typically be called in the certificate
       callback.

       An application wishing to support multiple certificate chains may call this function on
       each chain in turn: starting with the one it considers the most secure. It could then use
       the chain of the first set which returns suitable flags.

       As a minimum the flag CERT_PKEY_VALID must be set for a chain to be usable. An application
       supporting multiple chains with different CA signature algorithms may also wish to check
       CERT_PKEY_CA_SIGNATURE too. If no chain is suitable a server should fall back to the most
       secure chain which sets CERT_PKEY_VALID.

       The validity of a chain is determined by checking if it matches a supported signature
       algorithm, supported curves and in the case of client authentication certificate types and
       issuer names.

       Since the supported signature algorithms extension is only used in TLS 1.2, TLS 1.3 and
       DTLS 1.2 the results for earlier versions of TLS and DTLS may not be very useful.
       Applications may wish to specify a different "legacy" chain for earlier versions of TLS or
       DTLS.

SEE ALSO

       SSL_CTX_set_cert_cb(3), ssl(7)

COPYRIGHT

       Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.